Information, Linux Distributions, OpenSourceSoftware, Security, Snort, Sourcefire

Packetcapture with Snort using the “tag” option

I did this several years ago, but when I switched to full packetcapture I did not have the need for catching pcap of traffic firing a rule.

You can do this with the tag option in Snort. If you want to know more, please read README.tag.

I will present you with a signature that will log the first 1000 bytes or 100 seconds (What ever comes first!) after the packet that triggered the event. Im looking for a SYN flag in a TCP session and I start my logging from there (0,packets means that there are no limits on amount of packets).

alert tcp any <> $HOME_NET any (msg:”GL Log Packet Evil-IP (”; flags:S; tag:session,1000,bytes,100,seconds,0,packets; classtype:trojan-activity; sid:201102011; rev:1;)

I use unified2 as output plugin for Snort (something that also Sourcefire 3D does IIRC), so I need to fetch the pcap from the unified log. Snort 2.9.0 and newer ships with a new tool that will help you here, u2boat. This will carve out the pcaps from the unified log:

# u2boat /var/log/snort/<unified.log.timestamp> /tmp/snort.pcap

From there, you can read the /tmp/snort.pcap with tcpdump or wireshark etc. or just fetch the evil-IP packets:

# tcpdump -r /tmp/snort.pcap -w /tmp/Evil- 'host'

If you love it in console, you can read the pcap with tcpflow etc:

# tcpflow -c -r /tmp/Evil-

I did could not seem to verify that the “0,packets” actually do work. I added the following line also to my snort.conf:

config_tagget_packet_limit: 0

But again, not sure if it works.

I wanted to do some more testing before releasing this blog, but it has been sitting around for a while, so If I play more with it and have something new, Ill post a new post 🙂

BTW, turning you Sourcefire 3D into a packetcapture device is easy 🙂 adding the rule as above, you can just click the “Download Packet(s)” Button in the Event Information/Packet Information view 🙂 Use such a rule with care though…

Information, Linux Distributions, OpenSourceSoftware, Security

10 years of….

January 2011 has its 10th birthday…

Did you know that started out as the website for GamelinuX, a linux distribution for gaming?
I never got a working release that I wanted to present to the public, and after 2 years of working on the GamelinuX distro, the project came to an halt, as my Master degree and personal life took too much time from hacking on the distro. The GamelinuX project got official dead in September 2001 :/ And thinking of it now… do I have copies of the Alpha CDs somewhere??? I should have, but I dont know where… :/

My first security related post was in July 2003, when Free-X released an exploit for Xbox, that would let you install linux on it…

In March 2007, the blog entered its current form, leaving phpnuke/drupal (and clones) for wordpress. has always been about Open Source and hacking (‘as in finding a way to make things work’). As I started to play with Linux in 1998, Linux has been my OS of choice since. My reasons for continuing to blog security related topics on this domain, was that “Game Linux” was for me also associated with “gaming linux”, meaning “hunting linux” – find ways to break it/exploit it.

I went online for the first time with my Linux machine in 1998, and went to IRC/EFnet and the channel #Oslo. I asked anyone if they where into hacking/cracking, and asked for pointers on where/how to best start reading and learning more about it. Not long after, some guy told me to look in my /root/ directory and there was a dir that had a dozen of exploits… I realized that I had been hacked, and decided then not to get back online before I knew more about how to protect my self. The sploit used, IIRC, was a buffer overflow in wu-ftpd that shipped with the Red Hat release then, and wu-ftpd was default enabled 🙂

I stayed offline for about 2 months with my Linux machine, using the university machines to read more about hardening linux, firewalling, IDS, HIDS and such… As long as I can remember, I have been interested in hacking/cracking and defending from it. So linux+security has been an active interest for ~13 years now, and with my first related job experience ~10 years ago working for a Managed Security Service Provider (MSSP).

Thinking back the last 15 years, it has been some good years. I love what I’m doing and I have no plans on quitting!

Debian, Information, Linux Distributions, OpenSourceSoftware, Security, Sguil, Suricata, Ubuntu

OISF Suricata 1.1.0 beta 1 debian package for Ubuntu 10.04

I also got time to put together a package for the latest version of Suricata, namely 1.1 beta1.

My plan was to stick to a stable version when OISF released 1.0.3, but they skipped that, and went for a 1.1 release instead.
As I also try to help out where I can, I don’t mind running beta software, and reporting bugs etc. when and if I can. I’ll probably pack beta2 and so on until OISF hits a stable release, and then I’ll stick with that in my gamelinux PPA. So until then, I hope you try out Suricata with me on the quest for a stable release 🙂

Read more about suricata 1.1 beta 1 here.

Debian, Linux Distributions, OpenSourceSoftware, Security, Sguil, Snort, Suricata, Ubuntu

Sourcefire daq-0.4 and Snort- debian packages for Ubuntu 10.04

Moving to the new Snort 2.9 version, it added dependencies on a new library, namely DAQ(Data Acquisition library) for packet I/O.

So the little extra of packaging a new deb (daq) and check snort-debian files that they where compliant to the new version, made me debianize Suricata instead, as I saw that as quicker way to get an IDS up and running on my new firewall at home.

Now that I have suricata in place, plus some extra time last night, and I see people struggling trying to install/upgrade to Snort 2.9 on Ubuntu, I could not help my self trying to be helpful, again…

So I made debian packages and put them in my Ubuntu 10.04 Lucid PPA on launchpad. I started a new clean debian package for Snort. Its not yet packed with “debian-easy-features”, so it just installs Snort, makes the directories and adds some default configuration files. I will improve this as I go.

DAQ is built with:

Build AFPacket DAQ module.. : yes
Build Dump DAQ module…… : yes
Build IPFW DAQ module…… : yes
Build IPQ DAQ module……. : no
Build NFQ DAQ module……. : no
Build PCAP DAQ module…… : yes

And Snort is compiled with:


So, if you add my PPA, you apt-get install snort version Pronto though, Snort will be out, and I’ll upgrade accordingly. Suricata will also soon be out in 1.0.3, hopefully this week. Maybe we get fresh releases from this Santa for both engines 🙂

Until then,

-*> Snort! <*-
Version IPv6 GRE (Build 92)
By Martin Roesch & The Snort Team:
Copyright (C) 1998-2010 Sourcefire, Inc., et al.
Using libpcap version 1.0.0
Using PCRE version: 7.8 2008-09-05
Using ZLIB version:

Information, Linux Distributions, nftracker, OpenSourceSoftware, Security

nftracker – The Network File Tracker…

To fulfill my dream of automatic carving of files from network traffic, I wrote nftracker. The software is not 100% done, but well enough to deserve a blog post and to get a wider audience for testing! Some more file signatures could be added, especially for “Content-Type: ” in http or smtp traffic.

( I know I could have done something similar just writing snort/suricata rules. I could even write a snort preprocessor.. But hey! )

I also want to graph info from nftracker, such as how many files of type X traverse my network today, last week, month, year, etc..

A common first question from people is: Does it also carve out the files?
Answer: No

At this point, I just want to know whats on the wire. It would be cool to also carve out the file and dump it to disk (patches are welcome 😛 ), but for now I use other tools to do this. First of all, I use OpenFPC to do full packet capture. Mostly I have been using tcpxtract and I have also tested I see it as a bigger task to take on TCP reassembly and carving out the file correct, especially when I already have the pcap of the session, I can handle that offline. I also recommend xplico btw.

Default, nftracker logs to /var/log/nftracker-csv.log. The logfile looks like this:

# timestamp,[ session ],FILE_TYPE
# timestamp,proto,src_ip,src_port,dst_ip,dst_port,FILE_TYPE


I hope the tool is useful for someone, ideas/comments and such can be mailed to me.
I hope you try it out!

Information, Linux Distributions, OpenSourceSoftware, Security

multicap – multi interface networkstream dump daemon

Two weeks ago, I was made aware of a new tool to do packet captures with that looks promising. The initial commit seems to be from 2010-10-27 from the looks of the git repo found here.

To test it,
git clone git://
cd multicap
autoreconf -i
sudo ./multicap -w /tmp/ -c $PWD/multicap.conf.dist

You will find your pcaps under /tmp/var/log/multicap/.

I specially like the possibilities with this tool, that I can read/interpret from the config file. You can do “multi-sniffing”, writing to different logfiles filtered on BPF, specify different interfaces, snaplength, log rotation… Take a look at the configfile to see what I mean.
This is a tool to keep an eye on!
The project is young it seems, as passing –help option to multicap does not say anything…
Looking at the code, I know why 🙂

// show_version(NULL);